A typical fluorescent lamp includes a sealed glass tube containing a rare earth gas, and an electrode at each end for striking and maintaining an electric arc through the gas. The electrodes are typically constructed as filaments to which a filament voltage is applied to heat the electrodes, thereby improving their capability to emit electrons. This results in improved electric arc stability and longer lamp life.
Typical prior art ballasts apply the filament voltages to the filaments prior to striking the arc and maintain the filament voltages throughout the entire dimming range of the lamp. At low end, when light levels are lowest and, consequently, the electric arc is at its lowest level, the filament voltages help maintain a stable arc current. At high end, when light levels are highest, and the electric arc current is at its highest level, the electric arc current contributes to heating the filaments.
FIG. 1 is a perspective view of an example gas discharge lamp fixture 100. The fixture 100 includes a ballast 102, lamp sockets 104, and a housing 106. The ballast 102 and the sockets 104 may be fixed to the housing 106. The lamp sockets 104 may be sized and situated within the housing 106 to hold lamps 108. The ballast 102 may have wires 110 to connect the ballast 102 to the sockets 104 for driving the lamps 108 and for providing heating current, discussed above. In practice, the ballast 102 may be wired by a fixture supplier, as is common in new construction, or it may be wired by an on-site installer, as is common in retrofit projects.
Some ballasts are manufactured with the expectation that certain of the filaments are to be wired to the ballast in parallel with one another. Sometimes, such a ballast may be installed such that the filaments are inadvertently “miswired” in series with one another. Other ballasts are manufactured with the expectation that certain of the filaments are to be wired in series with one another. Sometimes, such a ballast may be installed such that the filaments are inadvertently “miswired” in parallel with one another. Certain problems may arise when the filaments are miswired. Not all of these problems are immediately apparent, and symptoms of these problems, such as shortened lamp life, may show up much later.